It is well known within contaminated water treatment and management systems to provide ponds for collecting and treating a variety of contaminated water streams including but not limited to industrial waste water, municipal waste water and stormwater.
In the case of stormwater management systems, it is well known to provide upstream forebays or ponds which are intended to receive stormwater runoff, in large volumes and having large peak inflow rates. Such ponds typically act to perform an initial clarification of the stormwater to remove at least a portion of the sediment and/or other pollutants or contaminants carried with the runoff before routing the stormwater to additional downstream means for removing pollutants and particulates therein and ultimately into streams, rivers or lakes within the local watershed.
Stormwater ponds collect, clarify and transport runoff water throughout the local watershed. The ponds are a passive means of treatment as they are largely unmonitored and not actively managed. The collection, clarification and transport is generally accomplished through the configuration of the ponds, storage volumes within the ponds or cells contained within the ponds, flow paths connected therebetween, relative elevations of the interconnected ponds and the like. Vegetation in the ponds may assist with the clarification and transport processes as is known in the art.
Generally, the forebay or upstream collection pond is separated from downstream ponds by a berm or spillway which feeds at least partially clarified water to the downstream pond. The berm or spillway may or may not be submerged in the pond. Such spillways may be constructed of materials which act to filter the water therethrough, such as packed gravel or the like or may simply form a diversion or outlet through which the water is directed. Generally, the minimum water elevation in an upstream pond is governed by the minimum elevation of the spillway that serves as the upstream pond outlet. Typically, the spillway is at the periphery of the pond and can be a weir, a pipe or other means.
In the event of a storm, runoff water from the upstream pond typically overflows the spillway opening, carrying contaminants such as sediment and other contaminants therewith, thus contaminating the downsteam ponds.
Conventional ponds are often assumed to have a plug flow which is analogous to pipe flow wherein inflowing water displaces in situ water. Alternatively, conventional ponds are thought to have a well-mixed reactor flow pattern which assumes new water entering the pond is instantly mixed and diluted with the in situ water. It has been found however that neither conventional assumption appropriately describes the manner in which a pond typically functions. Conventional water ponds, designed based upon these assumptions, therefore suffer from reduced treatment effectiveness and may have undesirable effects such as sediment deposition in undesirable locations and concentration and periodic release of cumulative pollutants to downstream waters.
There is great interest in providing an upstream pond which is capable of receiving large volumes of contaminated water entering the pond at high inflow rates and which is capable of providing effective and predictable treatment while achieving a reduction in the downstream carryover of sediment, oils or other undesirable contaminants, relative to the current state of the art.